1. Field of the Invention
The present disclosure relates generally to viscometers and more particularly to highly accurate and portable digital viscosity testing devices deployable in the field for unidirectional testing, bidirectional testing, and/or oscillation testing of fluid, slurry, and/or gel viscosity.
2. Discussion of Background Information
Viscosity testing is useful in a number of applications including, for example, the production of liquid compositions, cement slurries, gels, well drilling mud, viscous food and/or beverage products, pharmaceuticals, cosmetics, consumer products, paints, crude oil, etc. Testing samples of viscous substances, especially substances produced in batches, requires a high degree of accuracy both in measurement and analysis to insure proper formulation of the viscous substance. For example, cement slurries employed in securing oil well casings require frequent monitoring and testing in accordance with exact procedures and testing device standards that are designed to prevent catastrophic failure.
Viscosity testing devices exist for industry applications and industries have generated precise equipment specifications and testing requirements. For example, American Petroleum Institute Standard (API) API 13B-1/ISO 10414-1 provides precise measurement device dimensions and instructions for employing a measurement device to determine plastic viscosity and yield point of water-based drilling fluids. Petroleum drillers apply this standard, for example, to testing the oil well drilling mud used in the formation of oil wells. In accordance with API 13B-1/ISO 10414-1, a viscosity testing device may employ a bob of diameter 34.49 millimeters within a concentric rotor sleeve which may have an inside diameter of 36.83 millimeters. When submerged in a test sample, the rotor sleeve rotates and fluid shear forces applied to the bob impart torque on a shaft suspending the bob. In turn, in most devices, the shaft connects to a torsion spring for measuring resistance.
Standard viscosity testers, such as those provided by Fann® Instrument Company, provide visual pointer and increment type scales for reading a scale output measurement determined by the torque imparted on the torsion spring. These visual, incremented measurement scales bounce and/or jiggle in response to the vibration of moving parts during testing, thereby requiring a best guess as to a center point within a reading range. Further adding to inaccuracy and inefficiency, such scale readings require additional calculations to determine viscosity and do not provide a direct, simply viewed output reading of viscosity. Additionally, these standard analog viscosity testing devices incorporate analog transducers that drift with time and temperature, adding to the inaccuracy of test results. Additionally, these standard measurement systems lack sufficient precision for accurately testing highly viscous substances.
The API standards further require sampling viscosity at various speeds of rotation of the rotor sleeve. Most standard devices require that a user turn off the system motor and manually change gears on a standard two-speed motor, further delaying test efficiency. Some devices even employ a hand crank for varying rotor speed under inherently inconsistent human power, thereby introducing the variable of human error into the testing process. Furthermore, most viscometers are unidirectional and fail to accommodate accurate, repeatable bidirectional and/or oscillation testing of materials, like gels, that require such testing to determine viscosity and setting rate.
A need, therefore, exists for a system that preferably adheres to existing API standards and enables reliable, accurate and efficient testing of a wide range of viscous substances and gels. A need further exists for such a system that is easily controlled to produce a reliable and repeatable precise response by a computer controlled drive system that automatically changes speed and functions continuously and without interruption while running through a programmed routine. A need exists for such a device in a portable form for use in harsh, often hot and humid field environments such as those on oil rigs or manufacturing floors.